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- a material used for binding aggregate to form a
mortar or a concrete. Ideally cement
should be strong, durable and reliable. The Romans (see pozzolana) had produced successful
cements - Vitruvius describes them - without apparently understanding how these properties were
achieved. From the middle ages, builders searched for a reliable material, particularly for
lighthouse building, and roman cement (so named because it was thought to be equal to that
produced by the Romans), limestone and clay, burned and powdered, was produced in 1796.
After a period of further experimentation, Joseph Aspdin produced the reliable portland cement,
essentially a mixture of chalk and clay burned at high temperature before being powdered. Aspdin
thought his product looked like the famous portland limestone, and could be a cheap substitute
for this material, and this proved to be the case. Unfortunately it was quickly taken up by the
victorians for repointing, patching, refacing etc, usually with disasterous effect. Over the years
the product has been much improved but the name has survived.
Portland cement is often referred to as OPC - ordinary portland cement, to distinguish it from
masons cement which is white in colour, and weaker than opc which is grey, and, no matter what
colour of sand is used, unless a pigment is added, makes a grey mortar. Masons cement does
express the colour of a sand when used in mortars. Warehouse set is the term used to describe
cement that has set solid in its bag due to being stored in damp conditions.